The charging of ion exchange resin particles with uranyl ions is an early stage in the production of nuclear fuel particles for fuel elements for nuclear reactors.
The ion exchange resin particles of a cationic ion exchange resin have diameters of about 0.6 millimeter and, upon charging with uranyl ions, are converted into nuclear fuel particles in respective carrier bodies. In general, the uranyl-ion-charged particles are dried in air at temperatures slightly above 100.degree. C. and then are coked in a protective gas atmosphere at temperatures between 300.degree. and 1200.degree. C. The particles are sintered to uranium oxycarbide nuclear fuel particles at temperatures up to 1800.degree. C. This process is described, for example, in U.S. Pat. No. 3,438,749 for the production of plutonium oxide particles.
For an especially high concentration of uranium in particles of weakly acidic cationic ion exchange resins, mainly two principal parameters must be taken into consideration, these parameters being mutually related. The two parameters are the concentration of uranyl ions in the uranyl nitrate aqueous solution, which should be as high as possible, and the pH of the uranyl nitrate solution.
It has already been described in German Patent DT-PS No. 2,324,792 (see U.S. Pat. No. 3,800,023) that the uranium concentration and the pH value in the uranyl nitrate solution can be adjusted by the addition of UO.sub.3 powder. The UO.sub.3 powder must, however, be produced separately since the uranium is generally present as an aqueous uranyl nitrate solution.
In the Oak Ridge National Laboratory publication ORNL-TM-4955 of 1975, there is described a process in which the pH value is established by extraction of the nitrate ions from the solution with a liquid anion exchanger in a special extraction column. Apart from the extraction apparatus for the uranyl nitrate solution, this process requires the regeneration of the extraction agent. In addition, the uranium concentration of the uranyl nitrate solution must be held constant by evaporation of the solution. The process is thus associated with expensive apparatus and with high operating costs.